摘要:

A numerical study is conducted to investigate a new method of transition control by periodic suction‐blowing. It is shown that significant reduction in the amplitudes of two‐ and three‐dimensional finite‐amplitude disturbances can be obtained by the application of this method to transition in plane channel flow.

ISSN:0031-9171    

DOI:10.1063/1.864774

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A method is proposed to measure the dip in potential in the thermal‐barrier region of a tandem mirror. Plasma waves at a frequency near the plasma frequency of the cold electron component of a two‐temperature plasma are enhanced by the plasma Cerenkov effect, and can thus be used to scatter a laser beam. The measurements of cold plasma density as a function of position provide a sensitive measurement of the potential depression.

ISSN:0031-9171    

DOI:10.1063/1.864775

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The steady‐state drag of evaporating or condensing droplets in low Reynolds number flow is computed. Droplet drag in air is obtained for five representative liquids (water, methanol, benzene, heptane, octane) for a range of ambient temperatures, pressures, and vapor concentrations. The drag is in general increased for a condensing droplet, and decreased for an evaporating droplet. The changes in drag can be quite large and depend in detail on the degree of evaporation or condensation, and on the individual liquid and vapor properties. The present results are used to test the existing experimentally derived correlations of Eisenklam and Yuen and Chen in the low Reynolds number regime. The Yuen and Chen correlation is found to be quite successful, but only in the case of condensation or mild evaporation. An improved correlation is suggested for evaporating droplets.

ISSN:0031-9171    

DOI:10.1063/1.864776

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Linear stability of the one‐dimensional flow between infinite vertical coaxial cylinders induced by heating the inner cylinder is considered for various ratios &kgr; of the inner radius to the outer radius, and for Prandtl numbersPappropriate to air and water. For air withP=0.71 the least stable disturbance is nonaxisymmetric for &kgr;<0.44 and is axisymmetric for &kgr;>0.44, and in either case the instability is due to the action of the shear forces. ForP=3.5, the situation is similar, except that the asymmetric shear mode is superceded by an axisymmetric instability driven by buoyancy forces for 0.03<&kgr;<0.16. Wave speeds, wavenumbers, and critical Grashof numbers for these cases and for the case of zero Prandtl number are given.

ISSN:0031-9171    

DOI:10.1063/1.864777

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The propagation of steady pressure disturbances through a liquid containing small gas bubbles is investigated numerically. The equations of continuity and motion, together with the complete bubble dynamics equation, are employed. The analysis takes into consideration the effects of relative translational motions between the bubbles and the liquid. The results show the possibility of oscillatory shock waves that start with a steep rise in pressure followed by a relaxation region wherein the pressure exhibits damped oscillations about a final equilibrium value. For strong shocks, the predicted frequencies of pressure oscillations are so high that they may be unsusceptible to measurement. For weak shocks (p2/p1<2), the predicted wave forms are in agreement with the results of previous theories.

ISSN:0031-9171    

DOI:10.1063/1.864778

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Theoretical background is given for the separability of turbulent unsteadiness into the coherent and the chaotic. A method of nonlinear separation of variables applied to the turbulent correlation equation yields a fluctuation equation having two temporal operators representing coherent and chaotic unsteadiness. This equation is compared with the equation of fluid dynamic stability with regard to similarity in form and difference in physical content. It is stressed that the equation is essentially complex, and that the nonlinear term representing triple correlation substantiates continuous energy cascade towards lower frequencies as well as higher ones. A Fourier transform of this equation yields a Navier–Stokes equation for variables with physical meaning distinct from the ordinary ones.

ISSN:0031-9171    

DOI:10.1063/1.864779

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

An improvement of the eddy‐viscosity representation for Reynolds stress is made from the statistical viewpoint. The Reynolds stress is calculated with the aid of the two‐scale direct‐interaction formalism, and its deviation from the eddy‐viscosity representation is found under general mean flows. This result theoretically elucidates the noncoincidence of the zeros of Reynolds stress and mean strain, which is frequently observed in asymmetric turbulent shear flows.

ISSN:0031-9171    

DOI:10.1063/1.864780

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Two kinds of minimum enstrophy vortices in two‐dimensional flows are found by variational analysis. Each represents the ideal limit of a selective decay of enstrophy with energy and angular momentum or circulation, respectively, remaining fixed. For each, the vorticity is confined to a disk whose radius is determined by the fixed integrals. The definition of the vortices assures a large degree of stability, but many questions about their formation and destruction have not yet been answered.

ISSN:0031-9171    

DOI:10.1063/1.864781

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

An expression for the spectral emissivity of spontaneous synchrotron radiation for a plasma which consists of both thermal and suprathermal electron components is derived using the complete relativistic cyclotron resonance condition. The expression is valid over all angles of propagation. The result is applied to the study of the emission of radiation from an energetic population of electrons with a loss‐cone distribution in a relatively low‐density plasma (i.e., the electron plasma frequency is less than the cyclotron frequency).

ISSN:0031-9171    

DOI:10.1063/1.864782

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A theoretical, numerical, and experimental study is made of the behavior of the ponderomotive effect for rf frequencies close to the particle gyrofrequency. Near gyroresonance the stopping potential is found to be small rather than infinite. The interaction is not adiabatic, and heating results both in the parallel and perpendicular directions. This behavior is explainable in terms of the finite transit time of the particle through the localized rf structure. A perturbation theory that includes finite transit time is found to be in good quantitative agreement with both the numerical study and the experimental results.

ISSN:0031-9171    

DOI:10.1063/1.864761

出版商:AIP    

年代:1984

数据来源: AIP